Low-temperature oxidation of nitrided iron surfaces

The low-temperature (<150 K) oxidation of nitrided iron surfaces exposed to oxygen and water was probed using X-ray photoelectron spectroscopy (XPS), reflection absorption infrared spectroscopy (RAIRS), and mass spectrometry (NIS). During exposure of nitrided iron surfaces to oxygen, iron oxynitride (FexNyOz), nitrosonium ions (NO+), as well as nitrite/nitrito- and nitrate-type species were observed. The production of nitrite/nitrito and nitrate species is taken as evidence for the existence of oxygen insertion chemistry into the iron nitride lattice under these low-temperature oxidation conditions. No molecular nitrogen was produced during reactions with oxygen or water in contrast to oxidation studies on other transition metal nitrides. Upon annealing the oxidized overlayer, nitrogen desorbs exclusively as nitric oxide (NO) between 250 and 400 K. In contrast to oxygen, the reactivity of nitrided iron surfaces toward water was limited to the production of adsorbed N-O species.